fee vs fixed cost

fee and fixed cost both are nouns.

Word	Noun	Adjective	Verb	Adverb
fee	Yes	No	Yes	No
fixed cost	Yes	No	No	No

As nouns, fixed cost is a hypernym of fee; that is, fixed cost is a word with a broader meaning than fee:

fee: a fixed charge for a privilege or for professional services
fixed cost: a periodic charge that does not vary with business volume (as insurance or rent or mortgage payments etc.)

Other hypernyms of fee include fixed charge, fixed costs.

fee (noun)	fixed cost (noun)
a fixed charge for a privilege or for professional services	a periodic charge that does not vary with business volume (as insurance or rent or mortgage payments etc.)
an interest in land capable of being inherited

fee (verb)	fixed cost (verb)
give a tip or gratuity to in return for a service, beyond the compensation agreed on